/**
 * hashcash.ts — Proof-of-Work for VaaS DoS protection
 *
 * Red Team Fix #8: Requires unauthenticated API callers to present a
 * valid PoW token, making volumetric DoS economically infeasible.
 *
 * Uses WebCrypto (crypto.subtle) for Cloudflare Workers compatibility.
 *
 * Challenge format: `${dateHourUTC}:${clientIdentifier}`
 * The client must find a nonce such that SHA-256(challenge + ":" + nonce)
 * has `difficulty` leading zero hex characters.
 *
 * Default difficulty: 4 (approx 65,536 attempts, ~100ms on modern hardware).
 */
/** Default number of leading zero hex chars required. */
export declare const DEFAULT_POW_DIFFICULTY = 4;
/**
 * Generate the current date-hour challenge component.
 * Format: YYYYMMDDHH (UTC).
 */
export declare function getDateHourUTC(date?: Date): string;
/**
 * Build a challenge string from the date-hour and client identifier.
 */
export declare function buildChallenge(clientIdentifier: string, date?: Date): string;
/**
 * Find a nonce such that SHA-256(challenge + ":" + nonce) has `difficulty`
 * leading zero hex characters.
 *
 * @param challenge  The challenge string (e.g. "2026021223:192.168.1.1")
 * @param difficulty Number of leading zero hex chars required (default: 4)
 * @returns          The nonce string that satisfies the PoW
 */
export declare function generatePoW(challenge: string, difficulty?: number): Promise<string>;
/**
 * Verify that a nonce satisfies the PoW requirement.
 *
 * @param challenge  The challenge string
 * @param nonce      The claimed nonce
 * @param difficulty Number of leading zero hex chars required (default: 4)
 * @returns          true if the PoW is valid
 */
export declare function verifyPoW(challenge: string, nonce: string, difficulty?: number): Promise<boolean>;
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